An AlGaN/GaN high electron mobility transistor (HEMT) device, which is a power semiconductor device mainly used in fields that require high output, is bonded by a wire bonding method or a flip-chip method. The GaN (gallium nitride) HEMT device as a power semiconductor device has high output of several W to 100 W or more. For this reason, the GaN HEMT device generates a large amount of heat and therefore, needs to emit heat well. Meanwhile, an RF HEMT needs to have small parasitic inductance.
Therefore, the high-output RF HEMT device is preferably flip-chip bonded due to advantages such as good heat emission characteristics and small parasitic inductance and needs to be designed to have a structure capable of emitting heat well at the time of designing the device. In addition, at the time of manufacturing a module, a substrate on which the HEMT device is mounted needs to be designed and manufactured as a substrate having a material and a structure that emits heat well.
However, a size of an active region in which a source, a drain, and a gate of the HEMT device are formed is as small as about 20 μm and therefore, in order to bond the active region using a bump, the bump formed on a substrate needs to be formed to have a size of 20 μm or less and a via also needs to be formed to have a size of 20 μm or less. In this case, the via may be formed on an LTCC substrate so as to have a size of about 20 μm but it is difficult to fill a via hole of an inner diameter of 20 μm with metals. Therefore, the present disclosure proposes a method for forming a via for solving the above problems.